1. Field of the Invention
The invention relates to a fixed type constant velocity joint used in power transmission systems for automobiles and various industrial machines, for example, and adapted to only allow working angle displacement between two shafts on the driving and driven sides.
2. Brief Description of the Prior Art
The fixed type constant velocity joint is available, for example, in the UJ (undercut free) type. This fixed type constant velocity joint has a construction comprising a joint outer ring having an inner spherical surface formed with a plurality of circumferentially equispaced axially extending track grooves, a joint inner ring having an outer spherical surface formed with circumferentially equispaced axially extending track grooves paired with the track grooves in the joint outer ring, a plurality of balls disposed in ball tracks defined by cooperation between the track grooves in the joint outer and inner rings, a cage having pockets for holding the balls disposed in the ball tracks, and a receiving member formed with a concave spherical surface disposed in the bottom of the joint outer ring to axially support the outer peripheral surface of the joint inner ring.
The assembling procedure for this fixed type constant velocity joint is as follows. First, the cage is fitted in the joint outer ring to assume its normal position, and then the joint inner ring is axially inserted and pushed in until it abuts against the bottom of the joint outer ring. Thereupon, the balls are axially inserted into the cage pockets along the track grooves in the joint inner ring, whereby they are fitted in the track grooves in the joint outer ring. Thereafter, the joint inner ring is pulled back toward the open end of the joint outer ring, whereby the joint inner ring assumes its normal position while the balls are fitted in the track grooves in the joint inner ring (refer to, for example, Japanese Patent Kokai No. Heisei 6-193645 (pp. 4–6, FIGS. 6–9, and FIGS. 15–18), which is hereinafter referred to as Patent Document 1).
Further, other fixed type constant velocity joints include the BJ (Ball Fixed Joint) type. This fixed type constant velocity joint has substantially the same construction as that of the UJ type described above. That is, it has a construction comprising a joint outer ring having an inner spherical surface formed with a plurality of circumferentially equispaced axially extending track grooves, a joint inner ring having an outer spherical surface formed with a plurality of circuinferentially equispaced axially extending track grooves paired with the tracks in the joint outer ring, a plurality of balls disposed in ball tracks defined by cooperation between the track grooves in the joint outer and inner rings, and a cage having pockets for holding the balls disposed in the ball tracks.
The assembling procedure for this fixed type constant velocity joint is as follows. First, the cage is inserted into the joint outer ring with the center axis of the cage disposed orthogonal to the central axis of the joint outer ring. After this cage insertion, the cage is turned by 90° to bring the central axis of the cage into coincidence with the central axis of the joint outer ring. And the pockets in the cage are opposed to the track grooves in the joint outer ring and balls are inserted into all of the pockets. Thereafter, the central axis of the joint inner ring is brought into coincidence with an extension of the central axis of the joint outer ring having received therein the cage having the balls inserted in its pockets, and with the two central axes held coincident with each other, the joint inner ring is pushed into the cage (refer to, for example, Japanese Patent Kokai No. Heisei 7-98023 (pp. 2–3, FIGS. 1–4), which is hereinafter referred to as Patent Document 2).
In this connection, with the fixed type constant velocity joint disclosed in Patent Document 1, the assembling method therefor results in shallowing the track grooves, thus reducing the torque load capacity. That is, in the assembling of this fixed type constant velocity joint, in order to make it possible, after insertion of the cage into the joint outer ring, to insert the joint inner ring into the cage and push it to the bottom of the joint outer ring, the outer diameter of the joint inner ring is set smaller than the inner diameter of the cage. Here, since the outer diameter of an intermediate shaft fitted to the joint inner ring is of specified value, the track grooves in the joint inner ring will be shallowed if the outer diameter of the joint inner ring is reduced. This results in a problem that the torque load capacity of the constant velocity joint becomes smaller.
Further, with the fixed type constant velocity joint disclosed in Patent Document 1, the construction is such that the concave spherical surface of the receiving member disposed in the bottom of the joint outer ring axially supports the outer spherical surface of the joint inner ring. Since the concave spherical surface of the receiving member axially supporting the joint inner ring in this manner is positioned around the joint central axis and its support range is narrow, it is difficult to retain the constant velocity property during operation at a large operating angle, producing problems including vibration and abnormal sound, and a large relative displacement between the concave spherical surface of the receiving member and the outer spherical surface of the joint inner ring; thus, there is a fear that the heat generating rate increases.
Further, with the fixed type constant velocity joint disclosed in Patent Document 2, its assembling method is such that in pushing the joint inner ring into the cage with respect to the joint outer ring receiving the cage, the elastic deformation of the joint inner or outer ring is utilized. It is difficult to control the amount of elastic deformation of the joint inner or outer ring, and if the amount of elastic deformation is too large, the assemblability is degraded, with an excessive load applied between the balls and the tracks, tending to damage the area of contact between the two members, leading to a fear that the durability is lowered.
Further, according to the assembling method for the fixed type constant velocity joint disclosed in Patent Document 2, the central axis of the joint inner ring is brought into coincidence with an extension of the central axis of the joint outer ring, and with the two central axes held coincident with each other, the joint inner ring is pushed into the cage. In the case of the BJ type constant velocity joint in the Patent Document 2, the track groove bottom of the joint inner ring is rounded to make it easy to push the joint inner ring into the inner diameter of the cage, which cage, with balls inserted in its pockets, is received in the joint outer ring. If it is applied to the constant velocity joint of the UJ type, however, the track grooves in the joint inner ring of the constant velocity joint of the UJ type have a straight bottom, and since this straight bottom is positioned on the insertion side of the joint inner ring, the straight portions of the track grooves in the joint inner ring are large in relation to the inner diameter of the of the cage, which, with balls inserted in its pockets, is received in the joint outer ring, making it very difficult to push in the joint inner ring, degrading the assemblability.